1. Technical Field of the Invention
The present invention relates to a tandem type color image forming apparatus for forming a color image by providing image forming stations arranged with charging means, image writing means and developing means at a surrounding of an image carrier for respective colors along a transfer belt and passing the transfer belt through the respective image forming stations.
2. Description of the Related Art
In a related art, according to an image forming apparatus using an electronic photography technology, a photo conductor constituting an image carrier is charged by charging means, a latent image is formed by irradiating light in accordance with image information onto the charged photo conductor, the latent image is developed by developing means and the developed toner image is transferred onto a record medium to form an image.
According to the image forming apparatus using electronic photography, when the apparatus is used for a long period of time, it is necessary to interchange a photosensitive drum, replenish or interchange a processing agent, adjust, clean, interchange others (charger, cleaner vessel or the like) and such maintenance operation is in fact difficult for other than a service man having specialized knowledge.
Hence, according to an image forming apparatus using an electronic photography image forming process, there is adopted a process cartridge system for forming an electronic photography photo conductor and processing means operated to the electronic photography photo conductor integrally into a cartridge, and making the cartridge attachable and detachable to and from a main body of the image forming apparatus. According to the process cartridge system, maintenance of the apparatus can be carried out by a user per se without depending on a service man and therefore, the operability can significantly promoted. Therefore, the process cartridge system is widely used in the image forming apparatus.
In a related art, there is a color image forming apparatus of a tandem type aligning a plurality of photosensitive drums in one raw. According thereto, while carrying to transport a transfer member by an electrostatic transfer belt tensioningly hung by a plurality of rollers, by 4 pieces of photosensitive drums arranged along a path of transporting the transfer member, toner images comprising yellow, magenta, cyan, black are successively transferred onto a sheet and a color image is formed by overlapping respective colors (see, JP-A-2000-276030).
Attention is attracted to the constitution in recent years since printing can be carried out at high speed. However, since respective colors are formed by 4 pieces of the photosensitive drums, in comparison with a color image forming apparatus having a constitution of overlapping colors on a single photosensitive drum by way of four of transport paths for respective colors, with regard to rotational driving of the photosensitive drums, further accuracy is requested. Further, in such a kind of apparatus, maintenance is made to be easy to be carried out by unitizing an image forming mechanism to constitute a process cartridge and constituting the process cartridge attachable and detachable to and from a main body of the image forming apparatus.
According to the image forming apparatus, in order to attach and detach the process cartridge, it is necessary to cut to separate an image carrier and a drive transmitting mechanism and there is a concern of failing in forming an image and destructing a part when the process cartridge is not correctly engaged therewith in reinserting the process cartridge. Therefore, an easiness of attaching and detaching the cartridge to and from the apparatus main body and a certainty in an engaging state thereof are requested.
However, in the case of the cartridge of a photo conductor and developer integral type of the related art, a drive source of the photo conductor requesting a rotational accuracy is constituted by a system separately from a system of driving the developer or the cleaning means, drive forces of respective driven members are transmitted by coupling means and therefore, there poses a problem that a drive force transmitting mechanism becomes complicated and there is constructed a complicated constitution in attaching and detaching the drive force transmitting means in attaching or detaching the cartridge owing to a problem of phase matching or the like.
According to the image forming apparatus of a related art, driven motors are individually provided respectively for driven members for driving a photo conductor, for driving developing means, for driving a transcribing roller and so on. When the drive motors are arranged for the respective driven members in this way, the apparatus becomes large-sized to constitute a factor of an increase in cost, and therefore, there is also carried out a system of driving a plurality of driven members by a single drive motor. JP-A-2003-35984 discloses an image forming apparatus in which a plurality of photo conductors are driven by a singe drive motor and which is connected by a plurality of drive gears of the photo conductors and a drive gear of a developing roller. Further, JP-A-2003-131464 discloses an image forming apparatus in which a photo conductor and a developing apparatus are driven by branching a drive force of a single drive motor and which is provided with a clutch for switching to transmit a drive force of a fixing apparatus.
However, according to a constitution disclosed in JP-A-2003-35984, there poses a problem that a number of idle gears is large, which effects a significant influence on an image quality from a view point of an accuracy of the gear, further, since driving of a developer is branched from a middle of driving a photo conductor, respective loads thereof effect influences on each other. Further, according to a constitution disclosed in JP-A-2003-131464, driving of the fixing apparatus is switched by using the clutch means and therefore, there poses a problem that a complicated structure is constituted.
Further, according to a color image forming apparatus, a full color image is formed by overlapping toner images of respective colors and therefore, in order to promote an image quality, it is necessary to adjust a condition of driving the respective image forming stations.